1. Field of the Invention
This invention relates generally to apparatus for absorbing, storing and releasing thermal energy. More particularly, it is directed to compact light weight apparatus which is suitable for thermal energy storage at the location of demand, such as within a room of a private dwelling, and which can meet that demand utilizing an intermittent primary energy input.
2. Prior Art
Heat storage reservoirs are known and have been applied to the storage within a dwelling of thermal energy from an intermittent primary energy source, such as solar heat, and to the recovery of that stored energy during periods when the primary energy source is unavailable. Such reservoirs likewise have been utilized to reduce the cost of the primary energy, such as by employing electricity as the primary energy source only during off-peak hours; i.e., during periods of low demand when reduced rates are in effect. Among the more widely used energy storage materials are water, rocks and gravel, which store energy as sensible heat. Because of the great weight of the necessary quantities of such materials, it has not been possible to locate them in or near the living rooms of the dwelling which require the stored energy. Typically, these storage materials have been employed in a central bulk storage system which is located in the basement and which has heat exchange tubes coiled thru the mass of such material with pipe or duct connections to both the primary energy source and to each of the rooms. Since the stored energy demand is not usually in the basement, a great deal of insulation is required to prevent unwanted losses to the basement air. The cost of installing such system in a new structure is extremely high and is prohibitive when retrofitting an existing structure.
The volume and weight of a central thermal energy reservoir for a private dwelling may be greatly reduced by using for energy storage materials having a high latent heat of fusion, such as those described in U.S. Pat. Nos. 2,677,243, 2,856,506 and 3,320,408. While an improvement over the use of water or stone, these systems also are not entirely satisfactory. Suitable heat of fusion salts are often rather corrosive to the heat exchange tubes which coil through the mass of salt, and their low thermal conductivity makes it necessary to use a much larger than theoretical quantity of salt in a system which cycles within a 24 hour period. In addition, these salts have a limited useful life, and replacement (by pumping when hot and liquid or by chopping and shoveling when cold and solid) is costly, dirty and requires a lengthy shutdown of the entire heating or cooling system.